1. Field of the Invention
The present invention relates to a method of detecting a pinhole at a portion where pipes are jointed together by welding.
2. Description of the Related Art
FIG. 2 is a schematic view of a test article before pipes 1 and connecting members 2 are welded together. FIG. 3 is a schematic view of the test article after the pipes 1 and connecting members 2 have been welded together. The test article is typically a frame for use in a television cathode-ray tube. The principle of a conventional method of detecting a pinhole at a welded portion of an article will be described with reference to FIG. 4. First, air 6 compressed under a pressure of between 1.5 and 2.0 Kgf/cm.sup.2 is supplied both to the test pipe 1 and a leak-free master pipe 5 which is identical in shape to the test pipe 1 and has no pinholes. A pad 4 is attached to the test pipe 1 to surround an opening 3 (see FIG. 3). Two solenoid valves 7 and 8 are, thereafter, closed. Under the circumstances, if a pinhole is formed in the test pipe 1, then a slight change in pressure in the test pipe 1 takes place in several seconds. A differential pressure sensor 9 is then operable to sense the difference between the pressure in the test pipe 1 and the master pipe 5.
However, the pad 4 is subject to deformation when the pressurized air 6 is supplied. This causes leakage of air from the pad 4 and erroneously determines that there is a pinhole in the test pipe 1, regardless of the fact that no such pinhole is formed in the test pipe 1. Also, there may be a differential temperature between the test pipe 1 immediately after welded together and the master pipe 5. This differential temperature results in a corresponding differential pressure between the test pipe 1 and the master pipe 5. Consequently, a test result erroneously shows that there is a pinhole regardless of the fact that no such pinhole is formed in the test pipe 1. Appropriate measures should be taken to clean the pressurized air so as to inhibit oil mist or other foreign substances from entering into the pipes.